Osseous Structures

The osseous anatomy of the subaxial cervical spine is relatively constant, with the exception of C7, a transitional vertebra at the cervicothoracic junction. The posterior vertebral body ventrally, the pedicles laterally, and the laminae posteriorly form the boundaries of the spinal canal ( Fig. 34-1 ). Each vertebral body has an endplate superiorly and inferiorly. As the superior endplate extends from midline laterally, it slopes upward to form the uncinate process. The uncovertebral joint of Luschka is formed by the concave uncinate process of the inferior vertebra with the convex lateral inferior endplate from the suprajacent vertebral body. This is an important landmark when performing anterior discectomy or corpectomy.

Osseous anatomy of the subaxial cervical spine. A, Typical vertebral body viewed from above. B, Viewed from the left side. Cervical pedicles (6) are very short and extend at a medial angle from the superior articular process (1). The lateral mass (consisting of the superior [1] and inferior [7] articular processes] is rhomboid in shape when viewed from the lateral view. The superior surface of the vertebral body (5) is raised at the posterolateral corners to form the uncovertebral joints.

The transverse process extends from the pedicle laterally and anterior to the lateral mass. Unique to the cervical spine, within the transverse processes, is located the foramen transversarium through which the vertebral artery typically ascends beginning at C6. This particular anatomic feature allows for safe placement of pedicle screws into C7, which is discussed in detail later in the chapter.

Another feature of the vertebrae unique to the cervical spine is the lateral mass. The lateral mass forms the dorsal surface of the vertebra lateral to lamina. The lateral mass superiorly is bordered by the superior articular facet and inferiorly by the inferior articular facet. The subaxial cervical facets are oriented like shingles on a house. That is, the inferior articular facet of the cephalad vertebra is dorsal to the superior articular facet of its infrajacent vertebra ( Fig. 34-2 ).

Shingling of the facets in the subaxial cervical spine. The rhomboid-shaped facets overlap in a “shingling” pattern in the subaxial cervical spine. This is well visualized in the sagittal computed tomography reconstructions of the right ( A ) and left ( B ) facets. Note the left-sided C5 to C6 facet fracture-dislocation ( B ). On the axial cuts of the normal C3 to C4 level ( C ), note the shingling pattern of the facets, the superior facet of C4 is anterior to the inferior facet of C3. At the level of the injury, note that the right-sided facets have maintained their alignment, with the superior facet of C6 being anterior to the inferior facet of C5 ( D ). However, on the left, the C5 inferior facet is anterior to the C6 superior facet.

The lamina borders the lateral mass medially, which then slopes posteromedially, converging with the contralateral lamina to form the spinous process. Cervical spinous processes are often bifid except for C7. C7 typically has the most prominent spinous process of the subaxial cervical spine and is usually an easily palpable landmark.

Nonosseous Structures

The intervertebral disc borders the respective endplates of the superior and inferior vertebrae. It contributes significantly to stability of the vertebral disc motion segment. The nucleus pulposus is at the center of the disc and surrounding the central pulposus is the tougher fibrous annulus fibrosus.

Anterior elements are the anterior longitudinal ligament (ALL), intervertebral disc, vertebral body, intertransverse ligament, and posterior longitudinal ligament (PLL). The ALL runs longitudinally along the entire length of the spine anterior to the vertebrae or vertebral bodies. The ALL along with the anterior vertical fibers of the annulus fibrosus serve as important restraints to hyperextension. These anterior annular fibers typically fail in extension before the failure of the stronger ALL.

The PLL runs longitudinally along the posterior aspect of the vertebral bodies the entire length of the spine. Because of its more posterior location, the PLL resists flexion moments with strength similar to the ALL. The PLL thins laterally, and the posterior annular fibers are relatively weak compared with anterior annular fibers at the same level, which likely contributes to the relatively common occurrence of disc protrusions and herniations in this region ( Fig. 34-3 ).

Ligamentous anatomy of the subaxial cervical spine when viewed from lateral ( A ) and from above ( B ).

The posterior elements are defined as the structures posterior to the PLL. These include the facets, laminae, and spinous process, as well as the associated soft tissue structures, which include the ligamentum flavum, facet capsules, and interspinous and supraspinous ligaments. The ligamentum flavum extends from the anteroinferior surface of one lamina to the superoposterior surface of the inferior lamina. Although elastic in young people and resistant to flexion, with the aging process, the ligamentum hypertrophies and stiffens and may be a source of posterior impingement with anterior distraction injuries.

The cervical facet capsules in this region are patulous and do not restrict motion until extremes of flexion are reached. However, adjacent joints and capsules of levels not being fused should not be disrupted during posterior surgical exposures because this risks adjacent-segment instability.

The ligamentum nuchae is a triangular fibrous membrane that overlies the supraspinous and interspinous ligaments and runs between the external occipital protuberance of the skull and the spinous process of C2 and C7. When the ligamentum nuchae was resected in a cadaveric model, cervical spine stiffness decreased by 27%, and flexion increased by 28% indicating the importance of this structure as a stabilizing force. The ligamentum nuchae, infraspinous ligaments, and supraspinous ligaments are restraints to flexion and fail at the lowest forces in biomechanical cadaveric studies.

The Concept of Biomechanical Stability of the Cervical Spine

Under normal physiologic conditions, the human cervical spine is extremely mobile, allowing a high degree of flexibility and rotational movement. However, the same reasons that the cervical spine is so mobile also contribute to its susceptibility to indirect injury mechanisms. Most motion in the cervical spine is caused by occipito-cervical (O-C1) and atlantoaxial motion (C1–C2). In vitro cadaveric studies have demonstrated each level of the normal subaxial cervical spine contributes 8 to 10 degrees of flexion and 3 to 5 degrees of axial rotation. In vivo magnetic resonance imaging (MRI) studies of healthy volunteers have found between 1.5 and 4.6 degrees of axial rotation at each subaxial level and lateral bending at each level to be between 1.9 and 5.7 degrees. C2 to C3 has the most lateral bending at about 5 degrees; however, this is not significantly different than at other cervical levels.

White and Panjabi defined spinal instability as “the loss of the ability of the spine under physiologic loads to maintain its pattern of displacement so that there is no initial or additional neurological deficit, no major deformity, and no incapacitating pain.” Therefore, according to this definition, the spine is stable if it can withstand loads during normal activity without severe pain, neurologic deficit, or major deformity. Much of the stability of the subaxial spine is based not on osseous structures but on the ligaments that hold them in place. This explains why dislocated facets are considered unstable even after closed reduction. The ligaments holding them in place have been disrupted and are not expected to heal with the strength needed to maintain stability.

Quantifying Instability

In the absence of obvious dislocation or subluxation, destabilizing injuries in the subaxial spine are often subtle. Spinal imaging, whether plain radiographs, computed tomography (CT) scan, or MRI, is often static. These imaging studies do not show the spine under conditions of motion, loading, or at the moment of injury. Flexion and extension lateral radiographs are effective at showing instability but are not indicated in the acute injury period. Therefore, we need other ways of deciding when a cervical spine injury is a stable injury or whether it is unstable. Furthermore, the concept of cervical spine stability versus instability is closer to a spectrum of stability rather than a clear-cut division. These concepts make diagnosing and effectively treating subaxial cervical spine injuries challenging.

Several different scoring systems for quantifying cervical spine instability have been introduced. White and Panjabi introduced a scoring system based on biomechanical and radiographic studies. The White and Panjabi checklist assigns points based on competence or disruption of the anterior and posterior ligaments, the amount of static and dynamic displacement based on a “stretch test” using cervical traction, the neurologic status of the patient, the diameter of the spinal canal, and the anticipated loads on the spine. A total score of 5 or more points constitutes an unstable subaxial cervical spine injury. The clinical utility and reliability of the system has been called into question and, furthermore, does not offer treatment recommendations.

The Allen and Ferguson system is based on six mechanistic patterns along with substages based on anatomic disruption. The major patterns are compressive flexion, vertical compression, distractive flexion, compressive extension, distractive extension, and lateral flexion. The Allen-Ferguson system has been shown to have poor interobserver reliability when all 21 phylogenies are used and only moderate interobserver reliability when only the six basic phylogenies are used.

The Cervical Spine Injury Severity Score is based on a scoring system for the four columns of the cervical spine: anterior, posterior, and two lateral columns ( Fig. 34-4 ). The anterior column includes the ALL, vertebral body, and PLL. The posterior column includes the laminae, spinous processes, ligamentum flavum, and nuchal attachments. A visual analog scale from 1 to 5 is used to assess each of the four columns with increasing scores for increasing displacement or disruption. The sum of scores can range from 0 to 20, with scores greater than 7 indicating the recommendation for surgical treatment of the injury ( Fig. 34-5 ). Studies have shown high intraobserver and interobserver reliability with use of the Cervical Spine Injury Severity Score at all levels of training and experience. Although the Cervical Spine Injury Severity Score is useful for quantifying stability, it does not offer a classification system for injuries.

The Cervical Spine Injury Severity Score. This algorithm can be used to quantify the mechanical stability of the injury with the goal of deciding on the need for operative treatment. The cervical spine is divided into four columns (anterior, posterior, and two lateral columns), and the severity of injury to each column is assessed using whatever imaging modalities are available (e.g., plain film radiography, computed tomography, magnetic resonance imaging). The severity of the bony or ligamentous injury to each column is then assigned a number according to the analog scale shown below the films, with 0 being uninjured, and 5 being the most severely injured. The sum of the scores for each of the four columns then represents the Cervical Spine Injury Severity Score.

Application of the Cervical Spine Injury Severity Score. This patient presents with a flexion teardrop fracture. The midsagittal computed tomography reformat ( A ) shows a fracture of the anterior body of C6, retrolisthesis of the C6 body into the spinal canal, and wide separation of the C5 and C6 spinous processes. Based on this, the anterior column injury was graded a 4, and the posterior column injury graded a 5. The left sagittal reformat ( B ) with axial cut (inset) shows the C5 to C6 facet dislocation, giving the left lateral pillar a score of 4.5. The right sagittal reformat ( C ) shows diastasis of the C6 to C7 facet, giving the right lateral pillar a score of 2.5. The sum of these four pillars is the Cervical Spine Injury Severity Score; in this case, it is 16. Scores greater than 7 indicate sufficient instability to warrant surgical stabilization.

The Subaxial Cervical Spine Injury Classification (SLIC) system is based on three different parameters: the injury morphology, the neurologic status of the patient, and the integrity of the discoligamentous complex (DLC). Morphology is divided into no abnormality, compression, burst, distraction injury, and a rotational or translational injury ( Table 34-1 ). The DLC includes the intervertebral disc, ALL and PLL, ligamentum flavum, interspinous ligament, supraspinous ligament, and facet capsules and can be classified as intact, indeterminate, or disrupted based on MRI interpretation. The neurologic status is divided into intact, nerve root injury, complete cord injury, incomplete cord injury, or continuous cord compression in the setting of a neurologic deficit. Points are assigned for each of these descriptions, and total points are summed; the higher the points, the more severe the injury. Multiple injuries are individually scored and not cumulative. The total score helps to guide operative versus nonoperative treatment with higher points indicating the need for surgery. The original SLIC system showed moderate interobserver reliability among experts in the field.

Examination

The principles of initial patient evaluation, including history and physical examination, cervical spine immobilization, and the Advanced Trauma Life Support protocol, are discussed in another chapter. Understanding the injury mechanism may help give a clue to the likely structures injured. If the patient was in a motor vehicle accident (MVA), the most common mode of subaxial injury, the evaluator should know if the patient was the driver, passenger, in the front seat, passenger seat, seatbelted, in a head-on collision, rear-ended, T-boned, at high speed, low speed, or ejected from the vehicle. In addition to fully understanding the injury mechanism, the assessment should decipher relevant patient factors and comorbidities. The examination should include a full neurologic examination, which is discussed in detail in another chapter.

Imaging

Static spinal imaging seen with radiographs and CT scan may underestimate the amount of displacement that occurred at the time of injury caused by the elastic recoil of the intact soft tissue anatomy. Radiographs and CT may give clues to severe injury such as pretracheal edema, but often these clues are subtle. MRI, which is often challenging to obtain in the acute period in severely injured patients, and flexion-extension radiographs, which also cannot be obtained normally in the acute period, are usually the most useful indicators of soft tissue injury.

General Management Considerations

Basic principles of treating subaxial cervical spine injuries are to prevent further neurologic injury, reduce fractures or dislocations, and provide stability to the spinal column.

If a neurologic deficit exists, the determination needs to be made as urgently as possible whether or not a continuous source of compression exists and whether it is from fracture fragments, dislocation or subluxation, or epidural hematoma. The timing of decompression and whether or not pharmacologic agents are indicated is discussed in depth in Chapter 31 .

The injury pattern will help determine the degree of mechanical stability and, along with the SLIC score, can help determine whether the injury merits operative treatment. With more unstable injuries, surgical fixation is indicated, but stable injuries can generally be managed nonoperatively. Any subluxation or dislocation in general should be reduced. Whether or not these should be reduced closed or open depends on patient factors and the presence of a neurologic deficit. This is discussed later in the chapter in more detail.

Important patient factors other than neurologic status to consider when deciding on treatment include the presence of other injuries; noncontiguous spinal injuries; and comorbidities such as heart disease, chronic obstructive pulmonary disease, and other diseases in which the patient may be at high risk for adverse events. Diabetes and smoking increase nonunion and infection risk. Body habitus may also influence the management decision. Polytraumatized patients are at greater risk of aspiration pneumonia, decubitus ulcers, urinary tract infection, deep venous thrombosis, pulmonary embolus, and other complications from prolonged intensive care unit stays. Therefore, operative management, which immediately provides internal mechanical stability to allow for greater mobilization, may decrease the burden of injury in the acute period.

Principles of Nonoperative Management

A variety of cervical orthoses are available, each of which has varying capacity to stabilize the spine. The most basic difference between the different options is that some are cervical orthoses alone that only brace the neck itself, and others are cervicothoracic braces that extend the brace to the thorax. Chapter 39 is devoted to cervical and cervicothoracic braces in more detail.

When a cervical orthosis is used as definitive treatment, upright radiographs should be obtained with the orthosis in place to ensure proper alignment is maintained. If there is significant displacement seen with the orthosis, operative management should be considered. Patients should be followed with serial radiographs beginning approximately 7 to 14 days after the injury to assure that the orthosis is fitting properly and to verify that halo pins if used are not loose or infected. Radiographs are obtained every 4 weeks up until approximately 12 weeks postinjury at which time flexion and extension lateral plain radiographs are obtained to make sure healing has occurred. If failure occurs any time in the course of nonoperative treatment, operative treatment should be considered.

Principles of Operative Management

For unstable subaxial cervical spine injuries, operative management is indicated in anyone medically stable enough to undergo surgery. Operative management allows for direct decompression of the spinal cord, anatomic reduction and realignment, rigid stabilization, and bone grafting to promote fusion. The timing of surgical intervention is discussed in Chapter 32 but early fixation of an unstable cervical spine injury with a neurologic deficit not only potentially improves neurologic recovery but likely decreases the complication rate in the acute hospitalization period.

Flexion Teardrop Fracture

The teardrop fracture is a “vertebral body fracture characterized by a triangular, or quadrangular, bone fragment derived from the anteroinferior vertebral body. Coexistent anterior cranial-caudal vertebral body height loss must also be present.” Flexion teardrop fractures are most commonly caused by MVAs or by diving into shallow water. They have also been associated with American football spearing injuries.

Flexion teardrop fractures occur with the head flexed and an obliquely downward axial force concentrated on the anterosuperior vertebral body. With increasing loading force, the anterior column fails in compression, with the fracture propagating through the caudal disc space and into the posterior column. The posterior elements may become distracted and eventually disrupted with fracture or ligamentous disruption (or both). The involved vertebra essentially is split into a caudal segment composed of the teardrop component anteroinferiorly and a cephalad segment composed of the posterosuperior aspect of the intact vertebral body and the posterior elements ( Fig. 34-6 ). Although the anterior fracture is typically the most obvious radiographic finding, the integrity of the ligamentous complex posteriorly determines the stability of the injury.

Force propagation in a flexion teardrop fracture. A, The coronal fracture line separates the anteroinferior vertebral body (the teardrop component) from the remaining posterosuperior body. The fracture can propagate posteriorly through the spinal cord and posterior column, causing disruption of the ligamentous complex or fracture, as seen here. B, Magnetic resonance image demonstrates spinal cord injury caused by fracture and compression from posteriorly displaced vertebral body of C7 and malaligned spinal column.

Compression Fracture

Compression fractures are “vertebral body fracture with loss of craniocaudal height. No involvement of the posterior cortical margin and no translational or rotational deformity are allowed.” Although common in the thoracic and lumbar regions of the spine in individuals with osteoporosis, compression fractures in the cervical spine are less common. Typically, when they occur in the cervical spine, compression fractures are caused by low-energy mechanisms in individuals with osteoporosis or those with metabolic bone disease. Compression fractures can also occur in conjunction with a flexion-distraction injury mechanism and facet fracture-dislocation. When cervical compression fractures occur from a high-energy mechanism, an MRI should be obtained to evaluate the status of the DLC to ensure that the facet joints did not sublux or dislocate and spontaneously relocate.

Burst Fractures

Burst fractures are defined as “vertebral body fracture with loss of craniocaudal height and involvement of the posterior cortical margin. This fracture pattern is often associated with retropulsion of bone fragments into the spinal canal.” The mechanism of injury is initially pure axial loading. With severe injury and axial loading, eventually the subaxial spine will buckle and flex or extend, which may cause fracture of the posterior elements or ligamentous disruption, respectively. The most severe burst fractures with retropulsion have a high likelihood of spinal cord injury.

Treatment Recommendations of Burst Fractures

Treatment is dictated by the severity of the injury and the neurologic status of the patient. Most patients with burst fractures with retropulsion have a neurologic deficit. Without retropulsion or neurologic deficit, the patient may be managed nonoperatively with a rigid external cervical orthosis with close radiographic follow-up to ensure maintenance of alignment and no kyphotic collapse ( Fig. 34-7 ).

A, A 49-year-old man involved in motor vehicle accident with multiple cervical spine fractures, including a C2 fracture, anteroinferior endplate fracture of C4, and burst fracture to C7 (Subaxial Cervical Spine Injury Classification [SLIC] morphology = 2). The patient was neurologically intact (SLIC neuro = 0). The sagittal computed tomography (CT) scan shows minimal retropulsion of the C7 vertebral body. B, Parasagittal CT scan revealed the facet joints to be reduced. C, Magnetic resonance image showed retropulsion of the C7 body without cord edema. The posterior ligamentous complex was intact (SLIC DLC = 0; total SLIC score: 2 + 0 + 0 = 2 → nonoperative). D, The patient was treated nonoperatively with cervical orthosis; at 22 months after the injury, all fractures had healed, and no kyphotic deformity was present.

With retropulsion and neurologic deficit, surgery is indicated based on the SLIC scoring system. The posterior elements may also be injured, and MRI and CT should be analyzed for disruption of the DLC. Surgery should involve direct decompression of the spinal cord via an anterior corpectomy, strut grafting, and plating. Biomechanical cadaveric studies have shown that this method of fixation provides adequate stability in this injury pattern; however, if there is evidence on MRI of posterior ligamentous disruption, consideration should be given to combined anterior and posterior fixation ( Fig. 34-8 ).

A, A 19-year-old woman was ejected from a vehicle and sustained a complete spinal cord injury at the level of C6 and multiple fractures, including a C6 compression fracture (Subaxial Cervical Spine Injury Classification [SLIC] morphology = 1), C7 burst fracture (SLIC morphology = 2), and T1 compression fracture. B, Magnetic resonance image shows spinal cord injury, retropulsion of the C7 vertebral body, and disruption of the posterior ligamentous complex (SLIC: 2 + 2 + 2 = 6 → operative). C, The patient underwent decompression through an anterior approach on the night of her injury with C7 corpectomy and partial T1 corpectomy with strut allograft and buttress plate. She then underwent posterior stabilization and fusion at a later time when more stable to prevent kyphotic collapse.

Clinically, in a retrospective study comparing halo immobilization or skull traction with anterior corpectomy and plating in patients with flexion teardrop or burst fractures, operatively treated patients were significantly more likely to recover at least one grade of motor function and had a mean lordosis of 2.2 degrees versus a mean kyphosis of 12.6 degrees in the nonoperatively treated group.

Facet Subluxation, Unilateral Facet Dislocation, Bilateral Facet Dislocation, and Facet Fractures

Facet subluxations, unilateral facet subluxations, and bilateral facet dislocations will be discussed as a group because the structures injured, the injury mechanisms, and general treatment guidelines are similar and are typically discussed together. Facet subluxations are “misalignment of two adjacent vertebrae resulting in less than full apposition of facet articular surfaces (unilateral or bilateral).” Unilateral facet dislocations are “disruption of a single facet joint in which the inferior articular process of the cranial vertebra has translated anterosuperiorly over the superior articular process of the caudal vertebra.” Bilateral facet dislocations are defined as “disruption of both facet joints in which the inferior articular processes of the cranial vertebra have translated anterosuperiorly over the superior articular processes of the caudal vertebra. This pattern of injury may be associated with comminution, or fracture, of the facet joint complex. Perched facets, in which the tip of the inferior articular process abuts the superior articular process, qualify as dislocations as long as there is no articular surface apposition.”

These injuries all share a similar flexion injury mechanism either from a sudden deceleration in a MVA or a fall onto the head in which the head flexes. The center of rotation of the flexion moment is anterior to the vertebral body, such that the posterior elements of the spine become distracted and fail. There is frequently a concomitant compressive force to the subjacent vertebral endplate.

Unilateral Facet Dislocations

Cadaveric studies have shown that unilateral facet dislocations are created when the neck was flexed and bent laterally with subsequent axial torque. Another study showed that pure distraction applied unilaterally coupled with axial rotation creates enough force to cause a unilateral facet dislocation without the addition of a separate flexion moment. A cadaveric study of nine specimens in which unilateral facet dislocations or fracture-dislocations were created found upon postinjury dissection facet capsular tears and annular disruption in all specimens. In eight specimens, the ligamentum flavum was injured, and the interspinous and supraspinous ligaments were stretched in three and four specimens, respectively, but never completely torn. Disruption of the annulus accounts for acute traumatic disc herniation with potential neurologic deficit that is often associated with these injuries.

Without CT scan, unilateral facet dislocations can be missed because often spinal malalignment is subtle ( Fig. 34-9 ). On CT, a unilateral facet dislocation demonstrates a rotational deformity with reversal of the normal position of the superior and inferior facets at the dislocated level ( Fig. 34-10 ). The axial CT will show the inferior dislocated facet of the cephalad vertebrae lying anterior to the superior facet of the caudal vertebrae. Sagittal CT scan will also reveal the typical appearance of the completely dislocated or perched inferior facet sitting anteriorly or on top of the caudal superior articular facet.

A 35-year-old man involved in motor vehicle accident. A, Lateral injury radiograph shows anterolisthesis of C3 on C4 and a “bowtie” appearance of the facet at this level. B, On the anterior-posterior view, there is loss of the spinous process at the rotated level because it is not an orthogonal view due to the rotation of the injured level. C and D, Computed tomography (CT) scan reveals unilateral facet fracture dislocation on the left and uninjured contralateral side ( E ). Axial CT scan demonstrates the rotational nature of the injury in which only one side is disrupted ( F ).

A, A 21-year-old male rugby player was injured in a game and complained of neck pain and paresthesias in the arms but was neurologically intact (Subaxial Cervical Spine Injury Classification [SLIC] neuro = 0). Computed tomography (CT) scan shows C6 to C7 bilateral facet injuries with a dislocated facet and an associated fracture ( B ) and a contralateral facet subluxation ( C ) (SLIC morphology = 4). D, Axial CT scan shows complete dislocation of the unilateral facet. E, Magnetic resonance image shows anterolisthesis with disruption of the discoligamentous complex (SLIC DLC status = 2). The patient was close reduced while awake and subsequently underwent posterior fixation and fusion (total SLIC score = 0 + 4 + 2 = 6 → operative).

Bilateral Facet Dislocations

Bilateral facet dislocations have 50% or greater anterior translation of the dislocated vertebral body. Bilateral facet dislocations with only mild displacement on static imaging studies often underestimate the degree of displacement at the moment of injury.

Pure distraction and flexion is likely to produce a pure dislocation of the facets ( Fig. 34-11 ). However, in actual real-life high-energy traumas such as MVAs, multiple force vectors can occur concurrently. The flexion-distraction mechanism, combined with torsion, lateral bending, compression, or translation, may produce various combinations of fractures or dislocations (or both) of unilateral or bilateral facets ( Fig. 34-12 ). Often the superior facet of the caudal vertebra is fractured and displaced into the foramen by the inferior facet of the cephalad vertebra. Patients may have a nerve root injury caused by the fracture impinging on the nerve root in the neuroforamen. Laminae and spinous process fractures may also occur concurrently with this injury.

Bilateral facet dislocation mechanism. With sufficient forward flexion with distraction ( A ), both facets can dislocate ( B ). With lesser distraction and more forward translation, the facets can fracture. C and D, A 29-year-old woman with bilateral facet dislocation after a motor vehicle accident with incomplete spinal cord injury (Subaxial Cervical Spine Injury Classification [SLIC] neuro = 4 [3 + 1 {neuro modifier for continuous cord compression}]). E, Axial computed tomography scan shows the inferior facet of the superior vertebra completely dislocated anteriorly to the superior facets of the caudal vertebra (SLIC morphology = 4). F, Magnetic resonance image shows a large traumatic disc herniation (SLIC DLC status = 2). Circumferential stabilization of bilateral facet dislocations offers the most rigid stability to prevent deforming forces due to discoligamentous disruption from causing late kyphotic collapse and resultant deformity (total SLIC score = 4 + 4 + 2 = 10 → operative) ( G and H ).

Different facet injuries that may result from various combinations of flexion, compression, and rotation. Different configurations of facet injuries can occur, depending on the extent and timing of the forces acting on the spine at the time of injury. The top row ( A–E ) demonstrates a spectrum of purely ligamentous injuries, starting from the normally aligned facet ( A ). The facet capsule may be disrupted with subtle widening ( B ), and greater soft tissue disruption leads to facet subluxation ( C ), perching ( D ), and frank dislocation ( E ). The bottom row ( F–J ) demonstrates various fracture patterns. Most commonly, the superior facet is fractured and pushed forward into the foramen ( F ). Superior facet fracturing can be associated with facet subluxation or dislocation as well ( G ). Less commonly, the inferior facet is fractured, a pattern that may be associated with extension injuries and that often compromises the ability to place screws into this segment ( H ). Both the inferior and superior facets may be fractured ( I ). Finally, significant comminution of the facet ( J ) may preclude stable screw fixation at this level.

Magnetic resonance imaging is the best study to elucidate the full extent of soft tissue injury associated with facet injuries. In a retrospective study of 48 patients with unilateral (25 patients) or bilateral (23 patients) facet injuries, the authors found high rates of disruption to the posterior ligamentous complex (posterior muscles, interspinous and supraspinous ligaments, ligamentum flavum, and facet capsules). Disc herniations occurred in 56% of unilateral facet dislocations and 82.5% of bilateral facet dislocations. Another study of 30 bilateral facet dislocations found the ALL to be disrupted 27% of the time and the PLL to be disrupted in 40% of cases; however, disc disruption occurred in 90% of these injuries. The study also found that when compared with findings at surgery, MRI was accurate in diagnosing 24 of 26 ligamentous disruptions.

Disc Herniations and the Reduction of Facet Dislocations

Perhaps the most controversial aspect of treating subaxial cervical spine trauma is the treatment of facet dislocations in the presence of a traumatic disc herniation. With reduction of the dislocation, there is a risk of displacing a traumatic disc herniation further into the spinal canal ( Fig. 34-13 ). This was illustrated by Eismont and colleagues, who reported a 33-year-old patient who became quadriplegic after open reduction of a bilateral facet dislocation from a herniated disc behind the C6 body, which required anterior discectomy and fusion. Much debate exists surrounding both closed and open reduction of these injuries and the risk of causing a spinal cord injury or worsening the neurologic status of the patient with the reduction maneuver.

A, A disc herniation associated with unilateral or bilateral facet dislocation. B, There is a risk of worsening of neurologic deficit or paralysis if the disc flips back into the spinal cord instead of reducing into the disc space with the closed reduction of the dislocation.

Disc herniations can be difficult to define, especially in the presence of dislocation. Vaccaro and colleagues defined a traumatic disc herniation to be present when material with signal intensity consistent with disc protrudes posteriorly to the posterior cortical line of the inferior vertebral body. Others have defined disc herniation in the setting of facet dislocation as any ventral spinal cord or nerve root compression caused by disc material. The presence of a neurologic deficit on presentation has been shown to correlate strongly with the presence of a disc herniation. The rate of reported disc herniation in the presence of facet dislocation varies considerably ranging from 18% to 62% with higher rates for bilateral than unilateral dislocation.

Whether or not to obtain a MRI before attempting reduction is controversial. In a retrospective study of 11 patients with unilateral or bilateral facet dislocations, nine of whom had neurologic injury, all had prereduction MRI. Postreduction MRI revealed three additional herniations and worsening of one of the two prior herniations. No patient sustained worsening of neurologic status. The study suggests that the presence of a disc herniation does not preclude an attempt at closed reduction if the patient is awake, alert, and cooperative.

In a complete spinal cord injury, the benefit of rapid reduction and indirect decompression of the spinal cord would seem to outweigh the knowledge gained from a MRI. In a neurologically intact patient with a facet dislocation, the knowledge gained from prereduction MRI may or may not be of particular benefit and may also dissuade the treatment team from performing the reduction closed if a disc herniation is present.

In a patient presenting with an incomplete neurologic deficit, the most likely cause of the deficit is a disc herniation. Realigning the spine needs to be weighed against the risk of causing the disc to retropulse into the spinal cord, further worsening the neurologic status of the patient. If MRI can be obtained rapidly as is often now the case in spinal cord injury and trauma centers, it is acceptable to obtain a prereduction MRI, although a traumatic disc herniation does not necessarily preclude a safe and successful closed reduction in an awake and alert patient. In awake and alert patients who have a complete spinal cord injury (American Spinal Injury Association [ASIA] type A), prereduction MRI can be bypassed given the risk–benefit analysis of realigning the spine in a timely fashion in a patient with minimal risk of worsening the neurologic condition.

To date, no permanent neurologic deficit has ever been reported in an awake and alert patient undergoing closed reduction of a cervical facet dislocation. An awake, alert, and cooperative patient can safely undergo attempted closed reduction in a closely monitored environment. If the patient is obtunded or if a reliable neurologic examination cannot be obtained, closed reduction should not be attempted. In awake patients, closed reduction offers the potential for earlier decompression of the spinal cord.

Closed reduction also potentially prevents the need for a multistage surgical procedure. If a disc herniation is seen on MRI, a logical alternative to closed reduction is first an anterior procedure to perform a discectomy followed by a posterior procedure to reduce the facet dislocation and finally an anterior procedure to perform a fusion of the disc space. With a successful closed reduction, only one procedure is usually necessary, an anterior decompression and fusion or a posterior fusion. This avoids prolonged operative time and blood loss in patients who are typically polytraumatized.

Technique of Closed Reduction of a Cervical Facet Dislocation

Contraindications.

Contraindications to closed reduction of cervical facet dislocations include an obtunded patient or one in whom a reliable neurologic examination cannot be obtained. Other contraindications include the inability to visualize the affected level on a lateral plain radiographic image. This is most often a problem in obese patients with a thick neck and at lower levels such as at C6 to C7 and the cervicothoracic junction. These patients require a MRI to rule out disc herniation followed by open reduction. Fractures at other levels of the spine, specifically the upper cervical spine, should be ruled out because they can displace with traction. Although a fractured facet at the injured level is not an absolute contraindication, it may make the chances of a successful closed reduction less likely. Unilaterally dislocated facets in some series have been shown to be more difficult to reduce than bilaterally dislocated facets, although this is not a contraindication to an attempt at closed reduction. A stiffening spine disease such as ankylosing spondylitis (AS) is also a relative contraindication to cervical traction unless a form of traction such as bivector traction is used to realign the cervical spine rather than to reduce a dislocated facet.

Positioning.

The setting for closed reduction should be in a highly monitored environment. The procedure can be performed in an emergency trauma room, the intensive care unit, or an operating room (OR). Intravenous analgesia and a mild sedative that can be titrated will calm the patient and also have an effect to relax tense and spastic neck muscles, making the reduction easier to obtain. Close monitoring of the airway and respiratory status is essential, and therefore an anesthesiologist may be required.

The patient is placed in the supine position on a bed or stretcher. The reverse Trendelenburg position is used to counteract the pull of increasing weight applied cranially. A roll can be placed between the scapulae and the shoulders taped to the foot of the bed to better visualize the lower cervical spine and provide countertraction.

Pin Insertion.

Stainless steel Gardner-Wells tongs are preferred as traction weights of greater than 80 lb can cause MRI compatible tongs to disengage from the skull. Local anesthesia is injected into the skin at the site of pin placement, approximately 1 cm above the pinna and in line with the external auditory meatus. Because exaggerating the deformity is necessary to loosen or disengage the dislocated facet or facets, placing the pins slightly posterior to the external auditory meatus may create more of a flexion moment. The pins must be below the equator of the skull; otherwise, they risk disengagement through cephalad creep from the skull with application of weight. Shaving is not normally performed, although the pins may be covered with bacitracin ointment or the skin may be prepped with chlorhexidine as prophylactic measures. When in proper position, the pins are tightened until the spring strain gauge protrudes outward 1 mm, flush with the knob of the pin. The side locking nuts are then tightened to hold the pins in place.

Traction Weight.

An initial traction weight of 5 lb followed by 10 lb is begun. Lateral radiographs are obtained after each weight application. The entire cervical spine should be examined closely on the lateral radiograph to assess for previously undetected injuries, including injuries to the craniocervical junction, which may distract with minimal weight application. The position of the head and neck on the plain radiograph should be evaluated to ensure that the proper traction vector is being applied. At this point, weight is added in 5- to 10-lb increments. At each weight increase, the following steps should be taken: a lateral radiograph is taken to examine for overdistraction of all disc spaces, defined as greater than 1.5 times that of adjacent uninjured levels, and a thorough sensorimotor examination should be performed and documented, looking for any changes in neurologic status that may have occurred with increased weight applied.

With increasing traction and distraction, the dislocated inferior facet of the upper vertebrae should become distracted enough to minimize or remove the presence of bony impingement between itself and the superior articular facet of the lower vertebrae. The final stage of the reduction can be accomplished by lowering the height of the traction pulley or by placing an interscapular bump beneath the patient. Either of these maneuvers should create an extension vector, which allows the facets to return back into proper alignment, with the inferior facet of the cephalad vertebrae lining posterior to the superior facet of the caudal vertebrae. Unilateral facet dislocations, because of the more complex coupled forces involved with the injury mechanism, may be more difficult to reduce with longitudinal traction alone. In these instances, a lateral bending and derotation maneuver may be performed by an individual experienced in the technique. To accomplish this, the physician places his or her hands around the traction tongs with the thumbs above the traction pin against the sides of the skull with the second through fifth finger tips applied to the back of the cervical spine. At the time of facet perch, a downward force is applied to the located facet, and a gentle axial distraction and rotational moment is applied to the dislocated facet in the direction needed for reduction. This maneuver is followed again by lowering the height of the traction pulley or by placing an interscapular bump beneath the patient ( Figs. 34-14 to 34-17 ).

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